The current state of the art in the provision of balanced salt solutions and saline solutions of the type used in surgical procedures is generally to package the solution in a polyethylene squeeze bottle which includes an adapter that receives an irrigation cannula. The bottles must be sterilized internally and externally and are packed individually in a preformed blister pack which is sealed with a Tyvek.TM. lid. Because low-density polyethylene melts at approximately 100.degree. C. it cannot be heat sterilized (heat sterilization requires a minimum of 121.degree. C.). Therefore, the common practice is to aseptically fill the polyethylene bottles with a sterile solution, pack and seal the filled bottles in the blister packages, and expose each package to sterilization by ethylene oxide gas. Polyethylene is permeable to ethylene oxide and the above process results in some build-up of the gas in the sterile saline solution. When there is such a build-up, a chemical reaction takes place which results in the formation of ethylene glycol and ethylene chlorhydrin, both of which are potentially dangerous irritants that are highly undesirable in eye or other surgical irrigation solutions.
There have been some attempts to create a steam-sterilized package for saline solutions, but most of the known attempts have been commercially unsuccessful. One of the attempts which did receive some commercial recognition was a steam-sterilized process, but because of the special handling required by steam-sterilization the resulting product was a package that did not resemble the preferred squeeze bottle.
The present invention is a method of filling and sterilizing an improved squeeze-type bottle which is packaged in a blister pack sealed with a Tyvek.TM. lid before being subjected to a steam-sterilizing procedure. Polypropylene was the chosen material because it is known that polypropylene lessens the transport of ethylene oxide into the sterile solution. Additionally, although the polypropylene does expand and contract during the sterilization process and is known to soften to some extent at 121.degree. C., applicant has found that by using certain novel procedures in the filling and sterilization stages, a highly improved package and product which overcomes substantially all of the shortcoming and disadvantages to known processes is obtained.
In addition to the use of polypropylene for the bottle and the cap, one of the novel steps in the present process is the introduction of a resilient silicone gasket or washer which is inserted into the threaded screw-type cap such that the gasket is positioned between the cap and the bottle top to absorb pressures which develop by expansion of the bottle and/or the cap. By absorbing these pressures, the silicone gasket prevents any deformation of the cap, of the cannula adapter, or the bottle, and substantially eliminates any leakage of the sterile fluid from the bottle during sterilizing. Although other rubber products might be used to form the gaskets, silicone is preferred because it is a pharmaceutically and medically accepted material known to be non-toxic.
Another novel step in the process includes the use of a preprinted, self-adhesive backed polyester label that is applied to the bottle approximately twenty-four or more hours prior to the filling and sterilizing processes. The labels are designed such that they extend no more than two-thirds of the circumference of the bottle because it has been found that wrapping the label any further around the bottle results in creasing and crinkling of the label. Further, it has been found that when the labels are placed on the bottles at least twenty-four hours prior to filling and sterilizing, the labels demonstrate a marked improvement in adhesion to the bottle.
With regard to the use of the polycarbonate blister pack sealed to a Tyvek.TM. lid, the use of these products in a package which is going to be subjected to steam-sterilization requires certain modifications to the sterilization operation. Polycarbonate is known to soften during application of heat and it has been found that the weight of the filled bottle is sufficient to cause the polycarbonate blister to deform and on occasion to cause the Tyvek.TM. seal to pop open. However, applicant has discovered that by placing the packages blister-side-up in the sterilization trays, the weight of the bottle is eliminated from the blister and thereby avoids damaging to the blister while the package is in the sterilization tray. The trays which are used during the sterilizing process are preferred to be a stainless steel wire mesh. The wire mesh is desirable in order to drain away as much of the condensed water as possible and stainless steel is preferred because of the ease of sterilizing the non-corrodable trays. When water does not drain away, the Tyvek.TM. seals do not tolerate long immersion and break away from the polycarbonate blister. Further treatment to the Tyvek.TM. involves the "zone-coating" of adhesive in the area where the Tyvek.TM. is in contact with the polycarbonate blister. By eliminating adhesive coating from the entire free portion of the Tyvek.TM. surface (that portion not in contact with the blister pack), the porosity of the Tyvek.TM. is not damaged and steam and air can flow into and out of the blister pack during the sterilization procedure.